1. Field of the Invention
This invention relates to a mixing and kneading device in a so-called internal mixer which performs a thorough mixing and kneading operation irrespective of the kind of materials.
2. Description of the Prior Art
The internal mixer is a batch type kneader suitable for the intermingling of rubber and one of indispensable facilitites in the rubber industry, for example, in tire manufacturers as a mixer suitable for mastification of rubber, carbon master batch kneading of rubber or kneading of a vulcanizing agent commonly known as pro-kneading.
A prior art internal mixer, as indicated in FIGS. 1 through 3, includes a pair of parallel rotors 2, 3 provided within a chamber 1 for rotation in opposing directions to each other, each of which has a long vane 4 and a short vane 5. Both vanes extend spirally about the axis of the rotors. The spiraling or screwing direction of the long vanes is opposite to that of the short vanes. Materials introduced via a hopper not shown are sent under pressure from a supply inlet 10 into a mixing chamber 7 by the breaking-into action of the rotors and the depressing action of a floating weight. After being subjected to the rolling action by the rotors, the materials are ground between the edges of the vanes of the rotors and the inside wall of a casing (viz. a chip clearance 6), advancing in the axial direction of the rotors. These events occur on the long vanes and short vanes independently of each other. Since the screwing direction of the long vanes differs from that of the short vanes, the materials run from the edge to the center with respect to the respective rotors and the mixed and kneaded materials are delivered from the bottom of the chamber.
Another prior art embodiment, as indicated in FIGS. 4 to 6, includes a so-called four-vane rotor having two long vanes and two short vanes; a total of four vanes on each of the rotors. It is well known that, while construction is substantially the same, the four-vane rotor has a double chip in comparison with the above described two-vane rotor, promoting microscopic dispersion of an additive and assuring a high degree of mixing and kneading efficiency.
In order to produce a homogeneous mixture, macroscopic dispersion also is of great importance whereby the materials are uniformly mixed with keeping a uniform density of an additive everywhere in the resultant mixture and a uniform density of the mixture itself. For example, failure to produce a homogeneous mixture of a vulcanizing agent in the pre-kneading step of the manufacture of tires results in unevenness of physical properties of final products and difficulties in manufacturing quality tires. While the proportion of steel radial tires with steel cords embedded in the tires to overall tires has been increased more and more from a safety standpoint in high speed driving, there has been a trend to employ as rubber for such steel radial tire used materials which are much more hard per se and it is therefore more difficult to obtain a homogeneous mixture and dispersion than with conventional rubber material. To this end the prior art internal mixer lacked satisfactory strength of the mixing and kneading device and sufficient dispersibility of various agents.